STORY ARCHIVE

Tsunami Buoy

The catastrophic Indian Ocean tsunami of 2004 was a wake-up call for Australia. Within hours of an earthquake deep beneath the Indian Ocean, a quarter of a million people in a dozen countries, were engulfed by the most catastrophic tsunami in recorded history.

It was a day that inspired Australian scientists to develop a better warning system. “There was a feeling of dread as we started hearing reports of deaths and they were climbing…30, 40, 50, 100,000 deaths”, says Dr Ray Canterford of the Australian Bureau of Meteorology.

Australia is not as immune from tsunamis as you might think. In fact, recent research of written records and geological history has revealed evidence of 58 tsunamis in Australia, most of them in the last 150 years.

Climb aboard as Australia’s first tsunami warning alarm is dropped into a deep ocean trench; a system so sensitive it can detect waves just one centimetre high in 6000 metres of water.

But how much warning will we have before the next tsunami hits? And what will we do when the alarm is raised? Mark Horstman meets the people and the technology behind the new Australian Tsunami Warning System.

TRANSCRIPT

Narration 8 o’clock on a Sunday morning. Within hours, nearly a quarter of a million people in a dozen countries are engulfed by the most catastrophic tsunami in recorded history.

Dr Ray Canterford It was a tragic wake-up call for most Indian Ocean countries. There was a feeling of dread as we started hearing reports of deaths and they were climbing. 30, 40, 50, 100000 deaths.

Narration A tsunami is born from vertical movement on the seafloor, most commonly when the violent shift of tectonic plates catapults the ocean upwards.

Dr Dale Dominey-Howes Its wavelength is somewhere between 100-200km and in deep water, a tsunami is travelling at 5-6-700km an hour. When the tsunami gets close to shore the front end of the wave kind of slows down and the back end of the wave, which is 100km away, starts to catch up. In fact the Tsunami might flood in land for 10-15 mins before it slowly withdrawing back out to sea.

Narration As the first step to figure out how often we can expect tsunamis to hit, Dale Dominey-Howes delves into history.

Dr Dale Dominey-Howes This is a simple map of the history of tsunamis in Australia. Since we started our research we’ve found evidence of 58 tsunamis.

Narration And most of these are from the last 150 years.

Mark Horstman Now 58 tsunamis might strike people as more than they expected for Australia?

Dr Dale Dominey-Howes Well it’s a lot more than I expected as well.

Narration That’s because our continent is girdled by deep trenches called subduction zones, where one tectonic plate grinds over another.

Dr Dale Dominey-Howes You can see from the dark orange this is an area where we would expect very large earthquakes to occur, and such large earthquakes have the potential to generate damaging tsunamis, so it presents a fairly major hazard to us.

Narration How much warning will we get of a tsunami tearing towards the capital cities of south-east Australia? Warning alarms on the sea floor would improve our chances. And one’s about to leave the CSIRO docks in Hobart. The Southern Surveyor is preparing to drop Australia’s first alarm into the nearest oceanic trench to our biggest capital cities. This first one goes into the south Tasman Sea, we’re going to position it just our side of the Puysegur trench, which runs from the mountain chains in New Zealand southwest…we really want it in there as a first warning point.It’s going to take this ship four days to get there. It would take a tsunami wave just 2 hours to get here. On board will be this DART2 warning buoy, which stands for Deep-ocean Assessment and Reporting of Tsunamis.

The US has set up a network of 30 of these buoys dotted around the Pacific rim, reporting to a warning centre in Hawaii.

We’ve gone with the US technology, they’ve put a lot of effort into it, and we’re learning from them in a cooperative arrangement. There are two parts to the deep ocean tsunami buoys. There’s a surface buoy with the communication packages to the satellites, and there’s a Bottom Pressure Recorder which sits at 4-6 km on the sea bottom.

Narration Not all earthquakes generate tsunami. The Bottom Pressure Recorder can tell us when they do. We have the pressure sensor in here – it’s measuring the upward pressure of the earthquake, plus when the tsunami comes along, it’ll measure the surface variations from the tsunamis to an accuracy of 1mm.

Narration Deep on the sea floor, that incredible sensitivity can detect a 1cm wave in 6km of water. And then the pressure recorder has to send its data by sonar to the buoy floating far above, which relays it to warning centres. Where this buoy’s going it’s a very rough part of the ocean…its got to withstand harsh conditions, we’re in the Roaring Forties where we’re putting this.

Narration Marine engineer Ross Hibbins is sweating on finding the right spot.

Ross Hibbins When you’re working out in the ocean, trying to deploy anything off a ship, the main issue from my point of view as Chief Scientist, is concern with safety. You’ve got two and a half tonne of equipment hanging around, treacherous conditions, sliding along the deck, lifting across, something could break.

Narration Five kilometres below is the Puysegur trench. This could be ground zero for a dangerous tsunami.

Dr Diana Greenslade This is an example of a magnitude 9 event on the Puysegur trench…we’ve imagined that the whole trench might rupture, we don’t know if that’s going to happen anytime soon or sometime in the future, it’s never happened in the past.

Narration Diana Greenslade uses computer models to predict the size of tsunamis from earthquakes in the subduction zones around Australia.

Dr Diana Greenslade We’ve got a database of 741 different scenarios, and we only know how accurate it is when there’s an actual event.

Narration When an earthquake is detected, they compare the computer scenarios with what the nearest DART buoy is actually sensing.

Dr Diana GreensladeThe difficult thing is we need to know exactly how deep the ocean is at every point at high resolution, and particularly around the coast, to be able to forecast what happens to the tsunami as it arrives at the coast.that just doesn’t exist for most of Australia.

Narration All the information ends up here. This is the nerve centre of Australia’s tsunami warning system. Chris Ryan is responsible for making the call.We’re aiming to have a warning out within 30 minutes of an earthquake happening.

Narration Every four weeks or so, an alert from the Pacific warning centre in Hawaii throws this normally quiet office into action.

Chris Ryan We’ve got an earthquake message here. How big is it Adrian?

Chris Ryan It appears to be 7.8 Critical things to look at are how far away it is and that determines how long it will take to reach the coast.

Chris Ryan Hawaii’s got it at 7.8. No Tsunami measured yet The key thresholds are: what’s the magnitude of the earthquake? Starts at 6.5, that’s the lowest we’re interested in here…once you get over magnitude 8, it could be the whole Pacific Ocean or whole Indian Ocean. With the confirmation of the DART buoys and running the tsunami models in our computers here, we’ll be able to …highlight the bit of coast where people really do need to worry.

Narration And when this happens, how will the population react?

Chris Ryan Our warnings are useless if nobody does anything with them. I think even an over-reaction is better than being caught by surprise.

Narration After the recent Solomon Islands earthquake, Dale worries we still need to learn to take the warnings seriously.

Dr Dale Dominey-Howes What we saw in April 2007, although warnings were given, many surfers still went down to the coast and wanted to surf the tsunami when it arrived. So what that tells me is that we scientists haven’t done our job properly in communicating and working with the public. And at present the budget in the Australian Tsunami Warning System doesn’t match the budget of the physical infrastructure.

Narration With a budget of nearly $70 million, much more will be spent on technology than education. Over the next few years, more buoys will be deployed along the eastern coast and in the Indian Ocean. Out in the Tasman Sea, the deployment of our first DART buoy goes perfectly. The next time they see it will be in two years to change the batteries.

Ross Hibbins To see the buoy go over the side is a real buzz. The fact that we’re putting something out in the ocean in an area that we don’t have any coverage that could detect a tsunami and potentially save lives we should be proud of that.

[Dr Dale Dominey-Howes was working at Macquarie University when this story was shot, not at the University of New South Wales as credited by Catalyst. Dr Dominey-Howes was Senior Lecturer at the University of New South Wales when this story was first broadcast.]